An image sensor is a semiconductor device that may convert optical images into electrical signals. The sensitivity of an image sensor may be increased by increasing the speed and efficiency of the conversion of an incident light signal into an electrical signal.
In order to obtain a brighter and clearer image, the sensor may use a micro lens to concentrate light in a photo diode. The lens may also help to prevent light from impinging on neighboring cells. When incident light is not focused on the photo diode, cross-talk affecting neighboring cells may occur, which may degrade an image. To increase the speed of an image sensor, a relatively high stacked metal layer may be required. However, a relatively high stacked metal layer may create a constraint on the focal length of the micro lens. In order to maintain the focal length while reducing the pitch, the lens shape may be maintained while reducing the height of the micro lens. This may result in difficulties in a fabrication process.